The Need for Food
Animal Survival
Standard Grade Biology
Learning Outcome 1
• Explain in simple terms why food is
required by animals.
Learning Outcome 2
• State the chemical elements present
in carbohydrates, fats and proteins
• Describe the simple structure of
carbohydrates, proteins and fats in
terms of simple sugars, amino acids,
fatty acids and glycerol.
You are what you eat!!
• In this lesson you will
– Look at what is a balanced diet
– Carry out food tests on
• Starch
• Glucose
• Protein
• Fat
– Discuss what happens if you don’t eat
a balanced diet
Balanced Diet
What is a balanced diet?
• Your diet must include five groups of
food substances
– Carbohydrates, fats, proteins, minerals
and vitamins
• It must also include water and fibre.
• A balanced diet is a diet that
provides enough of these
substances in the correct
proportions to keep you healthy.
Carbohydrates
• Carbohydrates give us
energy.
• Chemical elements – C, H
and O.
• Starch is made from simple
sugars.
Testing for glucose
1. Pour some glucose solution into a
test tube
2. Add a few drops of benedict's
solution
3. Heat in a water bath
Testing For Starch
• Put a few drops of
starch solution on a
spotting tile.
• Add a few drops of
iodine.
Proteins
• Proteins are needed for
growth and repair.
• Proteins are made from
amino acids
• Chemical elements – C, H, O,
N (and S)
Testing for Proteins
1. Put 2 ml of protein
solution in a test tube
2. Add 2ml of Biurets
reagent
Fats
• Fats are an energy store,
protecting vital organs and
providing insulation.
• Fats contain C, H and O
• Fats are made from a
glycerol molecule and three
fatty acids.
Testing for fat (the emulsion
test)
• Add a few drops of cooking oil into
a test tube
• Add 2cm3 ethanol and shake
• Add 2cm3 water and shake again.
What happens if you don’t
eat a balanced diet.
What is this cartoon
trying to demonstrate?
Can you think of any
examples of health
problems that arise
from not eating a
balances diet?
Give three examples and
explain the effects on
health.
Learning Outcomes 3
• State that digestion is the
breakdown of large particles of food
into smaller particles to allow
absorption into the blood stream
through the small intestine wall.
• Explain that digestion involves the
breakdown of insoluble food
substances into soluble food
substances
What happens to the food
we eat?
The gut as a production line
Learning Outcome 4
• identify in a diagram / model the main
parts of the mammalian alimentary canal
and associated organs (mouth, salivary
glands, oesophagus, stomach, pancreas,
liver, gall bladder, small intestine, large
intestine, appendix, rectum and anus)
• state the sites of production of the main
digestive juices in mammals (salivary
glands, stomach, pancreas, liver, small
intestine)
Digestion
• Digestion is the breakdown
of large, insoluble food
molecules into small,
soluble food molecules so
that they can be absorbed
into the blood stream.
Pupil Activity
• Label the diagram of the digestive
system.
– Use the textbook supplied to help if
needed
– Design a table to link the structure and
function of different parts of the
digestive system.
mouth
tongue
Salivary glands
oesophagus
trachea
liver
stomach
Gall bladder
Small
Duodenum
intestine ileum
appendix
pancreas
colon
Large
rectum intestine
anus
Mammalian teeth
The Need for food
Animal Survival
SG Biology
Learning Outcomes (5)
• To know the different structure and
functions of each type of tooth
• To understand the adaptations of a
herbivore, omnivore and a carnivore
to feeding.
Feeding in mammals
• Mammals have teeth which may be
used to bite pieces of food and to
chew it into smaller pieces before
swallowing.
• The shapes of teeth are suited to
their function.
– Incisors and canines are used for biting
– Premolars and molars are used for
chewing and crushing food.
Patterns of Teeth
Human Jaw
teeth
• There are different types of teeth, each
specially shaped to perform a particular
job.
– Incisor - A broad flat sharp tooth found at the
front of the mouth. Designed for biting and
cutting food.
– Canine - A sharp pointed tooth for piercing
flesh and tearing.
– Pre-molar & molar - A broad flat tooth with
many cusps. Its rough surface is used for
crushing, grinding and chewing food
Carnivore adaptations
• Look at the dog skull, and the
diagrams of a dogs skull.
• With the aid of a diagram – make
notes explaining how the dogs teeth
and jaws are adapted for a
carnivorous diet.
Herbivore adaptations
• Look at the sheep’s skull, and the
diagrams of a sheep skull.
• With the aid of a diagram – make
notes explaining how the sheep's
teeth and jaws are adapted for a
herbivorous diet.
Learning Outcome 6
• Explain the mechanism of peristalsis
• Explain how the contractions of the
stomach help in the chemical
breakdown of food.
Digestion of Food
• The digestion of food can either be
mechanical or chemical.
• Mechanical digestion includes
– Chewing
– Action of muscles in oesophagus, stomach and
small intestine
• In chemical digestion enzymes catalyse
the breakdown of larger food molecules
into smaller food molecules.
Digestion in the mouth and
oesophagus
• Chewed food is mixed with saliva in the
mouth
• Saliva contains
– Amylase is an enzyme which starts to digest
starch into sugars (maltose)
– Mucus helps soften the food making it easier
to swallow
• The bolus travels down the oesophagus
with the aid of peristalsis
Peristalsis in the gullet
Learning Outcome 7
• State that different enzymes are
responsible for the breakdown of
carbohydrates, proteins and fats.
• Give an example of an amylase, a
protease and a lipase. State their
substrates and products.
Digestion of Starch
• Take 2ml of 1% starch solution
– Test for starch
– Test for sugars
• Take 2 ml 1% starch solution, add
2ml 2% amylase solution
– Leave for 20 minutes
– Test for starch
– Test for sugar
Action of amylase on starch
• Put two drops of iodine solution into
all the wells on a white spotting tile
• Add 2ml 1% starch solution and 2ml
2% amylase solution to a test tube.
• Every minute, test the contents of
the test tube for starch.
• Write a conclusion on your results
Protein Digestion
• Protein digestion occurs in the
stomach and small intestine.
• Protease enzymes are produced by
the gastric pits in the stomach lining
or by the pancreas.
• In the stomach, hydrochloric acid is
also produced which provides the
optimum pH for trypsin to work (as
well as killing bacteria in food)
Protein Digestion
• Add 2ml of protein solution to three
test tubes.
• Number the test tubes 1, 2 and 3
1. Add 1ml HCl
2. Add 1ml Water
3. Add 1ml HCl
• Do not add the trypsin until last
1. Add 0.5 ml water
2. Add 0.5 ml trypsin
3. Add 0.5ml trypsin
Protein digestion
• Leave for 10 minutes
• Test each of the test tubes for the
presence of protein using Biurets
reagent.
• Explain your results.
Fat Digestion
• Milk does not dissolve in water, in the
digestive system, bile produce by the liver
(stored in the gall bladder) emulsifies fats
to give a larger surface area for enzymes
to work on.
• You are going to use phenolphthalein to
investigate the effect of bile on the
digestion of fat.
Fat Digestion
• Take 4 test tubes and number them
1, 2, 3 and 4.
• set up the test tubes as shown in the
table below.
Test tube
1
2
3
4
Milk
Bile
3 ml
0
3ml
0.5ml
3ml
1 ml
3ml
1ml
Water
1ml
0.5ml
0
0
Fat Digestion
• Add 5 drops of phenolphthalein to each
test tube
• Add sodium carbonate to each test tube
until the solution goes pink.
• Add 0.5ml of lipase to test tubes 1, 2 and
3.
• Add 0.5 ml water to test tubes 4.
• Observe your results. Try to explain what
you are observing.
Chemical Digestion
• Enzymes
– Are proteins
– Are produced by cells
– Change chemical substances into new
products
– Are “specific” to one substance
– Work best at their “optimum
temperature” (around 30 – 40o)
– Work best at an optimum pH
Digestive enzymes
• There are different types of digestive
enzyme
– Proteases break down proteins into amino acids
– Lipases break down fats into fatty acids and
glycerol
– Amylase breaks down starch (carbohydrase
enzyme) into maltose (sugar)
• Maltose is then broken down by maltase to form
glucose
Chemical Digestion
• There are also other substances in
the digestive system which help with
the breakdown of food.
• Hydrochloric acid
– Secreted by stomach
– Kills the bacteria in food
– Enzymes in stomach work best at a low
pH e.g. pepsin
Chemical Digestion
• Hydrogen carbonate ions
– Secreted by pancreas
– Neutralises acid, enabling enzymes in small
intestine to work
• Bile
– Produced by liver, stored in gall bladder,
secreted into small intestine
– Emulsifies fats (Larger surface area for
enzymes to work on)
Learning Outcome 8
• State that only small soluble molecules
can pass through the wall of the small
intestine.
• Explain how the structure of the small
intestine is related to its function.
• Explain how the structure of a villus,
including the lacteal and the blood
capillaries, are related to the absorption
and transport of food.
• Describe the role of the large intestine in
water absorption and elimination.
Digestion in the small
intestine
• 3 important liquids are added to the
food
– Pancreatic juice (carbohydrases,
proteases and lipases)
– Bile (neutralises acid and emulsifies fat)
– Intestinal juice (carbohydrases,
proteases and lipases)
What happens next?
Absorption in the ileum
• The small intestine is well designed
for absorption, it has
– Thin lining
– A good blood supply
– A very large surface area (about 9m2)
Absorption in the Villi
The Model Gut
A model of absorption
“the model gut”
Making a model gut
• Wash a 12cm length of visking tubing (A) in
warm water.
• Tie a knot in one end
• Fill the tubing with 10cm3 of starch and
glucose solution(B).
• Wash the outside of the tubing.
• Put it into a boiling tube containing DI water
(C) (holding it in place with a rubber band.
• After 20 minutes, test the surrounding water
for starch and glucose.
C
B
A
Comparing the model gut
with the villi
• Draw conclusions from the
experiment, explaining what the
results were, and how the model gut
represents the real situation
• E.g. what does the water represent,
what does the Visking tubing
represent, etc.
Large intestine and the
elimination of waste.
• A watery mix of enzymes and
undigested food (mainly fibre)
moves into the colon.
• Water is absorbed back into the
blood stream.
• Faeces are compacted in the
rectum and egested through the
anus.
The end
What do
they think
they are
looking at?
Learning Outcome 9
• To revise the learning outcomes
taught in this sub topic.
What happens to the food
we eat?
The gut as a production line